ABSTRACT Approximately one out of every three children and two out of every three adults have overweight or obesity. To date, the most successful treatment for child weight loss is family-based treatment for childhood obesity (FBT), which combines nutrition and physical activity education with behavior therapy strategies and parent management techniques targeted to shape healthy behaviors in both the child and parent. Unfortunately, not all children and parents respond and the majority regain most or all of their weight back. One of the challenges for families attempting to manage their weight is the current food environment, which is replete with high calorie, hedonic, low cost foods which make it incredibly easy to eat beyond nutritional needs. It is very possible that weight loss programs fail because current treatments inadequately target basic cognitive mechanisms that are inherently involved in how individuals interact with the current food environment. Overeating, or eating past nutritional needs, is theorized to be a result of the interaction between two basic cognitive mechanisms; physiological and psychological reward from food and the ability to inhibit impulses to overeat. We have developed a number of food-specific cognitive assessments which target specific vulnerabilities in people who have overweight and obesity. For this project, we propose to add assessments of reward and inhibition that include both self-report and task-based measurements among 260 parent/child pairs participating in two R01 projects evaluating 6-month FBT programs. Assessments will be conducted at baseline, 6-, 12- and 24-month timepoints. The primary aims of this study are 1) to determine behavioral and psychological phenotypes of reward and inhibition at baseline in children and parents and 2) to evaluate whether these phenotypes predict weight loss in both children and parents at 6-, 12- and 24-month timepoints. We will also compare behavioral and psychological phenotypes of reward and inhibition between parents and children, and we will 1) evaluate whether the interaction between child and parent phenotypes of reward and inhibition predict weight change at 6, 12- and 24-month timepoints, 2) evaluate whether parenting style interacts with child behavioral and psychological phenotypes of reward and inhibition, and 3) explore whether the behavioral and psychological phenotypes identified at baseline in children and parents change over time and whether these changes are associated with weight loss in children and parents. This project will collect crucial, unique data on both reward and inhibition aspects of cognition, in both children and parents participating in an FBT program. These data will allow the identification of specific cognitive phenotypes in children with overweight and obesity and their parents, and ultimately to develop targeted treatments that could be more effective with specific groups of children and parents.